April 2014
Beginner to intermediate
392 pages
14h 57m
English
Two basic types of sensors are triggered by variations in light. There is the active type and the passive type.
The Chronophotonic Lamp Controller that I described in Experiment 7 used a phototransistor, which is a passive sensor. It just sits and waits, measuring light from outside sources and changing its effective internal resistance accordingly.
Another common passive light-sensing component is a PIR motion sensor, where the P in the acronym stands for “passive” and the IR stands for “infrared.” These are commonly used to switch on lights or trigger alarm systems when they sense body heat from a person moving around.
PIR motion sensors are useful, but the complete units that you find in hardware stores ...